Help Your Roses Avoid Disease...

Roses have a lot to offer as terrific landscape plants with a wide diversity of habit, form, and shape and a long color season. Among some home gardeners, however, roses have acquired a reputation as garden prima donnas — delicate and temperamental but beautiful stars that are susceptible to attack by a number of diseases. Although good hygiene and preventive spraying can go a long way toward keeping diseases in check, you may find it preferable to plant tougher, more durable varieties that have built-in resistance.

Weather is one factor affecting the susceptibility of roses to disease. Cool temperatures and high humidity promote fungal problems, while hot, dry climates keep them at bay.

For example, if your climate is cool, humid, or rainy, you may find fungal diseases such as mildew especially difficult to control. Black spot, another fungal disease, is a significant problem in all regions of the United States except the arid West. If you live in a relatively humid area and lack the time to spray as often as recommended, disease-resistant plants are almost a necessity.

The list at the bottom of this section identifies some rose varieties that are the most resistant to rose diseases. (Note, however, that no rose is completely invincible.) In addition to these, virtually all members of the shrub rose classification resist rose diseases, as do most alba and damask roses, and species roses except those with yellow flowers.

Plant genetics also plays a role in a rose variety's ability to ward off disease. A rose's immune system consists of phenolic compounds that resist infection. Lack of moisture or nutrients can cause these protective chemicals to weaken, letting infection take hold.
In recent years, breeding efforts have resulted in the further development of varieties that are nearly impervious to disease. While the degree of disease resistance and shade tolerance will vary among classes, such as between a hybrid tea and a shrub rose, these newer rose introductions offer a wide variety of choices.
Knock Out, a shrub rose bred by William Radler and introduced by Conard-Pyle in 2000, is the epitome of these roses. It has shown nearly complete resistance to black spot and excellent resistance to other fungal diseases and some pests.

Now its relatives are making a splash. Blushing Knock Out, a lighter pink sport of the deeper cerise Knock Out, is a compact, hardy shrub. Carefree Sunshine, introduced in 2001, is one of the most disease-resistant yellow roses. And the newest family member, Pink Knock Out, carries the same black spot resistance.

For a complete list of "disease resistant" roses, go to Rose Secrets Revealed.